1. Field of the Invention
The present invention relates to a SIP (Session Initiation Protocol) exchange system which performs communication between SIP telephones to each other by using SIP call control and, more specifically, to a SIP exchange system which can display a telephone number of a called party that is communicating on a calling SIP telephone, even an incoming party is changed due to call forwarding or proxy response.
2. Description of the Related Art
A conventional telephone transmission system performs dialing call, incoming call, communication, displaying a telephone number of a called party, and the like between SIP telephones through SIP call control of SIP exchange equipment.
In the communication between SIP telephones, when a calling SIP telephone dials to a called SIP telephone as target (i.e., telephone number of the called SIP telephone); however, if “call forwarding” is preset in the called SIP telephone, the incoming call forwards to a SIP telephone of the call forwarding.
And, when a called SIP telephone is ringing for an incoming tone; however, if the user of the called SIP telephone can not or will not respond to the incoming call, a user of other SIP telephone operates “special number” to set “proxy service” and responds to the incoming call, then the SIP telephone of the proxy response will receive the incoming call.
A conventional SIP exchange system will be described below. FIG. 6 shows a configuration of a conventional SIP exchange system. In FIG. 6, a SIP exchange system 50 comprises, for example, SIP exchange equipment 51 and SIP telephones which comprises a SIP terminal 52a, a SIP terminal 52b, and a SIP terminal 52c. The SIP exchange equipment 51 and the SIP telephones are connected to a network NT.
The SIP exchange equipment 51 performs SIP call control on the SIP terminal 52a, SIP terminal 52b, and SIP terminal 52c. For example, when the SIP terminal 52a (telephone number “1000”) dials to a telephone number “2000”, the SIP telephone 52b receives the incoming call (i.e., ringing for the incoming tone). When the SIP telephone 52b responds the incoming call, the communication between the SIP terminal 52a and SIP telephone 52b becomes possible.
In this communication, the display of the SIP terminal 52a displays the called party number “2000”, and the display of the SIP terminal 52b displays the calling party number “1000”, so that the telephone number displayed on the one party corresponds with the other party of communication.
Next, a sequence operation will be described. In this operation, when the SIP terminal 52a dials to the SIP terminal 52b, the SIP terminal 52b is set “call forwarding” for forwarding to the SIP terminal 52c (telephone number “No. 3000”), or the SIP terminal 52c performs “proxy response” for the incoming call directed to the SIP terminal 52b. 
FIG. 7 shows a sequence diagram of call forwarding operation of an embodiment of a conventional SIP exchange system. In addition, a SIP terminal 52a, a SIP terminal 52b, and a SIP terminal 52c are represented as SIPa (No. 1000), SIPb (No. 2000), and SIPc (No. 3000) respectively.
In FIG. 7, the SIP exchange equipment 51 has previously been set “call forwarding” for forwarding from the SIPb (No. 2000) to the SIPc (No. 3000).
When the SIPa (No. 1000) dials to the SIPb (No. 2000), the display of the SIPa (No. 1000) displays the called party number “2000”. Then the SIPa transmits a calling message “INVITE (to No. 2000)” to the SIP exchange equipment 51, the SIP exchange equipment 51, which should forward the call to the party number “3000”, transmits the calling message “INVITE (to No. 3000)” to the SIPc (No. 3000).
Upon receiving the calling message “INVITE (to No. 3000)”, the SIPc (No. 3000) transmits a temporary reception response message “100 Try” to the SIP exchange equipment 51. The SIP exchange equipment 51 then transmits the temporary reception response message “100 Try” to the SIPa (No. 1000).
Subsequently, when the SIPc (No. 3000) transmits a coming ringing start message “180 Ring” to the SIPa (No. 1000) via the SIP exchange equipment 51a, the ringing tone (incoming tone) is generated in the SIPc (No. 3000), and the RBT (ring back tone) is generated in the SIPa (No. 1000).
Upon listening the ringing tone (incoming tone), the SIPC (No. 3000) responds the incoming call, and transmits an incoming response message “200 OK” to the SIPa (No. 1000) via the SIP exchange equipment 51.
Upon receiving the incoming response message “200 OK”, the SIPa (No. 1000) transmits an acknowledgement message “ACK” to the SIPc (No. 3000) via the SIP exchange equipment 51.
In this state, the SIPa (No. 1000) and the SIPc (No. 3000) move to the communication; the display of the SIPa (No. 1000) displays the party number “2000”, and the display of the SIPc (No. 3000) displays the party number “1000”.
Therefore, the display of the SIPc (No. 3000) displays the party number “1000” that corresponds with the party of communication; however, the display of the SIPa (No. 1000) displays the party number “2000” (number of the SIP b) that is different from the party of communication (SIPc (No. 3000)).
FIG. 8 shows a sequence diagram of proxy response operation of an embodiment of a conventional SIP exchange system. In addition, a SIP terminal 52a, a SIP terminal 52b, and a SIP terminal 52c are represented as SIPa (No. 1000), SIPb (No. 2000), and SIPC (No. 3000) respectively.
In FIG. 8, when the SIPa (No. 1000) dials to the SIPb (No. 2000), the display of the SIPa (No. 1000) displays the called party number “2000”, the ringing tone (incoming tone) is generated in the SIPb (No. 2000), and the RBT (ring-back tone) is generated in the SIPa (No. 1000). In this state, when the SIPc (No. 3000) dials a special number, e.g., “YZ” for “proxy response”, and transmits a calling message “INVITE (to the special number)” to the SIP exchange equipment 51, the SIP exchange equipment 51 then transmits an incoming response message “200 OK” to the SIPa (No. 1000).
When the SIPa (No. 1000) transmits an acknowledgement response message “ACK” to the SIP exchange equipment 51, the SIP exchange equipment 51 then transmits a response message “200 OK” to the SIPc (No. 3000).
Next, when the SIPc (No. 3000) transmits an acknowledgement response message “ACK” to the SIP exchange equipment 51, SIPa (No. 1000) and SIPc (No. 3000) initiate the communication.
On the other hand, the SIP exchange equipment 51 transmits an incoming cancel message “CANCEL” to the SIPb (No. 2000), and upon receiving a response message “200 OK” and a message “487 ReqCancel” from the SIPb (No. 2000), transmits an acknowledgement response message “ACK” to the SIPb (No. 2000). The SIPb (No. 2000) then stops the ringing (incoming tone stop).
In this state, the SIPa (No. 1000) and SIPc (No. 3000) move to communication; the display of the SIPa (No. 1000) displays the party number “2000”, the display of the SIPc (No. 3000) displays the “special number”.
Therefore, the display of the SIPc (No. 3000) displays the party number “special number YZ” different from the party of communication (SIPa (No. 1000)), and the display of the SIPa (No. 1000) displays the party number “2000” different from the party of communication (SIPc (No. 3000)).
And, the conventional SIP exchange system is known, as disclosed in Japanese Laid-Open Patent Application No. 2002-152224; hereinafter “patent document 1”, which is configured to provide “proxy response” (Refer to the sequence diagram of the incoming proxy response in FIG. 7 described above).
The conventional SIP exchange system performs the communication between the SIP telephones to each other by using the SIP call control; however, there is a problem that causes reduction in service, because, in the SIP call control until establishment of communication, the message to notify the final party number stays in the state of the call initiation. That is, even the party of communication in response to the incoming call is changed due to the call forwarding or proxy response, the display of the party number is not changed. Thus, there is unnatural in that the party number is not correspondence with the party of communication.
And, the telephony transmission system disclosed in the “patent document 1” also provides the proxy response; however, it would be predicted that the system becomes unnatural, because the telephone number is not changed to that of the incoming party that has been changed due to the proxy response (the display of the party number is not disclosed in the patent document 1).
The present invention intends to solve the problem. An object of the invention is to provide a SIP exchange system in which the display of the party number is correspondence with the final party of communication, even the party that responds incoming call is changed due to the call forwarding or proxy response.